U.S. patent number 9,423,794 [Application Number 13/700,318] was granted by the patent office on 2016-08-23 for control system for travel in a platoon.
This patent grant is currently assigned to VOLVO CAR CORPORATION. The grantee listed for this patent is Jonas Ekmark, Henrik Lind. Invention is credited to Jonas Ekmark, Henrik Lind.
United States Patent |
9,423,794 |
Lind , et al. |
August 23, 2016 |
Control system for travel in a platoon
Abstract
The present invention relates to a control system for travel in
a platoon (1), the platoon comprising a lead vehicle (L) and one or
more following vehicles (F.sub.1, F.sub.2, . . . , F.sub.i-1,
F.sub.i, . . . , F.sub.n) automatically following the lead vehicle,
the lead vehicle controlling the movement of the following
vehicles, each of the following vehicles and the lead vehicle
comprising communication means (10, 12), wherein the control system
comprises a common time base, which allows a control command
proposing an action to be communicated from the lead vehicle (L) to
at least one of the following vehicles (F.sub.1, F.sub.2, . . . ,
F.sub.i-1, F.sub.i, . . . , F.sub.n) in advance of a control point
(t.sub.c). The invention further relates to the use of a common
time base in a platoon and to a method to control travelling in a
platoon.
Inventors: |
Lind; Henrik (Torslanda,
SE), Ekmark; Jonas (Olofstorp, SE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lind; Henrik
Ekmark; Jonas |
Torslanda
Olofstorp |
N/A
N/A |
SE
SE |
|
|
Assignee: |
VOLVO CAR CORPORATION
(Gothenburg, SE)
|
Family
ID: |
42813107 |
Appl.
No.: |
13/700,318 |
Filed: |
May 30, 2011 |
PCT
Filed: |
May 30, 2011 |
PCT No.: |
PCT/EP2011/058788 |
371(c)(1),(2),(4) Date: |
May 02, 2013 |
PCT
Pub. No.: |
WO2011/151274 |
PCT
Pub. Date: |
December 08, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20130211624 A1 |
Aug 15, 2013 |
|
Foreign Application Priority Data
|
|
|
|
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May 31, 2010 [EP] |
|
|
10164446 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G05D
1/0295 (20130101); G08G 1/22 (20130101); G05D
1/0278 (20130101); G05D 1/021 (20130101); G05D
2201/0213 (20130101); G01S 2013/9325 (20130101) |
Current International
Class: |
G05D
1/02 (20060101); G08G 1/00 (20060101); G01S
13/93 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
|
10248469 |
|
Aug 2008 |
|
CN |
|
1708065 |
|
Oct 2006 |
|
EP |
|
11-339185 |
|
Dec 1999 |
|
JP |
|
2000-339600 |
|
Dec 2000 |
|
JP |
|
2008-003675 |
|
Jan 2008 |
|
JP |
|
2009-40351 |
|
Feb 2009 |
|
JP |
|
2009-157794 |
|
Jul 2009 |
|
JP |
|
2008018607 |
|
Feb 2008 |
|
WO |
|
Other References
Hewlett Packard Application Note 1272, "GPS and Precision Timing
Applications," May 1996. cited by examiner .
The International Search Report and Written Opinion issued on Aug.
9, 2011 in connection with PCT Application No. PCT/EP2011/058788.
cited by applicant .
Porche et al., "Real time task manager for communications and
control in multicar platoons" Intelligent Vehicles '92 Symposium,
Proceedings of the Detroit, MI, USA Jun. 1-29, 1992, New York, NY,
pp. 409-414. cited by applicant .
Office Action issued by the Japanese Patent Office on Sep. 1, 2015
in connection with related Japanese Patent Application No.
2013-512854 and English translation thereof, 9 pages. cited by
applicant.
|
Primary Examiner: Olszewski; John R
Assistant Examiner: Foster; Gerrad A
Attorney, Agent or Firm: Gesmer Updegrove LLP
Claims
The invention claimed is:
1. A control system for travel in a platoon, said platoon
comprising a lead vehicle and one or more following vehicles
automatically following the lead vehicle, said lead vehicle
controlling the movement of said following vehicles, each of said
following vehicles and said lead vehicle comprising communication
means, wherein said control system comprising a common time base,
wherein a control command is communicated from said lead vehicle to
at least one of said one or more following vehicles in advance of a
control point of time, the control command entails an action to be
executed by the one or more following vehicles at the control point
in time, the common time base is based on time signals from an
external clock where the time signals are received by the lead
vehicle and the one or more following vehicles simultaneously,
wherein if the time signals from the external clock cannot be
received, then the common time base is based on a last time signal
received from the external clock.
2. The control system according to claim 1, wherein the common time
base has a precision of at least 10 ms.
3. The control system according to claim 1, wherein a time gap
between two vehicles of said platoon is less than 0.6 s.
4. The control system according to claim 1, wherein, in case of
signals from said external clock being temporarily undeceivable, a
time base of an individual vehicle of said platoon is based on the
last signal received from said external clock and/or on a time
signal sent from said lead vehicle.
5. The control system according to claim 1, wherein said control
command is adapted to compensate for dynamic properties of said at
least one following vehicle and/or time delays within said
platoon.
6. The control system according to claim 1, wherein said proposed
action comprises an action expressed as a state control over time
for said following vehicle.
7. The control system according to claim 1, wherein said following
vehicle proposes to said lead vehicle a possible limited state
action instead of said proposed action according to said control
command sent from said lead vehicle.
8. The control system according to claim 1, wherein the control
systems further comprises a negotiation, which is used when a
candidate following vehicle wants to connect to said platoon, said
negotiation comprising sending of boundaries for state control of
said candidate following vehicle, and wherein said candidate
following vehicle is refused to connect to said platoon, if said
candidate following vehicle has a too limited state control
capability.
9. A use of a common time base in a platoon for controlling
travelling in the platoon, the platoon comprising a lead vehicle
and one or more following vehicles automatically following the lead
vehicle, said lead vehicle controlling the movement of said
following vehicles, each of said following vehicles and said lead
vehicle comprising communication means, wherein a common time base
allows a control command to be communicated from said lead vehicle
to at least one of said one or more following vehicles in advance
of a control point of time, the control command entails an action
to be executed by the one or more following vehicles at the control
point in time, the common time base is based on time signals from
an external clock where the time signals are received by the lead
vehicle and the one or more following vehicles simultaneously,
wherein if the time signals from the external clock cannot be
received, then the common time base is based on a last time signal
received from the external clock.
10. A method for controlling travelling in a platoon, said platoon
comprising a lead vehicle and one or more following vehicles
automatically following the lead vehicle, said lead vehicle
controlling the movement of said following vehicles, each of said
following vehicles and said lead vehicle comprising communication
means, wherein said method comprising the steps of (a) establishing
a common time base, (b) transmitting a control command from said
lead vehicle to at least one of said one or more following vehicles
in advance of a control point of time, the control command entails
an action to be executed to be executed by the one or more
following vehicles at the control point in time, the common time
base is based on time signals from an external clock where the time
signals are received by the lead vehicle and the one or more
following vehicles simultaneously, wherein if the time signals from
the external clock cannot be received, then the common time base is
based on a last time signal received from the external clock.
11. The method of claim 10 further comprising the step of: (c) said
at least one of said following vehicles acknowledging the receipt
of said control command to the lead vehicle; and the optional step
of: (d) said lead vehicle sending an execute demand.
12. The method of claim 10 further comprising the step of: (e) said
at least one of said following vehicles communicating a message to
said lead vehicle that said following vehicle is able or unable to
carry out said proposed action according to said control
command.
13. The method of claim 12, in the case able was communicated, said
method further comprising the step: (f) the lead vehicle
transmitting an execute command based on step b).
14. The method of claim 12, in the case unable was communicated,
said method further comprising the step: (g) said at least one of
said following vehicles communicating to said lead vehicle a
possible limited state action; and the optional step of: (h) the
method returning to step b) and said lead vehicle transmitting a
new control command based on said limited state action, or
alternatively said lead vehicle releasing said platoon.
15. The control system according to claim 1, wherein the common
time base has a precision of at least 1 ms.
16. The control system according to claim 1, wherein the common
time base has a precision of at least 100 .mu.s.
17. The control system according to claim 1, wherein said vehicles
prepare one or more actions in advance of the control point of
time.
18. The method of claim 10, wherein said vehicles prepare one or
more actions in advance of the control point of time.
Description
PRIORITY INFORMATION
The present application is a 371 national phase application of
International Application No. PCT/EP2011/058788, filed on May 30,
2011, that claims priority to EP Application No. 10164446.6, filed
on May 31, 2010.
TECHNICAL FIELD
The present invention relates to a control system for processional
travel in a platoon comprising a lead vehicle and one or more
following vehicles automatically following the lead vehicle. The
invention further relates to the use of a common time base in a
platoon and to a method for controlling travelling in a
platoon.
BACKGROUND OF THE INVENTION
Driving self-propelled vehicles in a convoy generally requires a
driver for each vehicle. As an alternative, so called platooning
may be used. A platoon comprises a lead vehicle and at least one
following vehicle. When the platoon moves, the lead vehicle
controls the movement of the following vehicles by means of
inter-vehicle communication. By using platooning the need to drive
the following vehicles may be eliminated. Further, the distances
between the vehicles of the platoon, i.e. the inter-vehicle
distances, may be shortened as compared to distances between
vehicles in normal traffic, thereby increasing transport capacity
of for example a road. Short distances between vehicles of a
platoon have also been proven to reduce air resistance, and thereby
reduce fuel consumption.
The document U.S. Pat. No. 6,640,164 B1, by Farwell and Caldwell,
discloses a system for remote control of self-propelled vehicles,
especially vehicles in a convoy. The lead vehicle takes a
succession of GPS coordinate positions along the way and broadcasts
them to a following vehicle, so that it can traverse the same
course as the lead vehicle.
Since the lead vehicle of the system disclosed in U.S. Pat. No.
6,640,164 B1 sends the GPS coordinates of the waypoints it has
passed, the control of the following vehicles is based on events in
the past, though in the recent past.
There is a desire to be able to make the inter-vehicle distances
even shorter than in existing platooning in order to increase the
above-mentioned positive effects. There is therefore a desire for
an improved control system for travelling in a platoon.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome or ameliorate at
least one of the disadvantages of the prior art, or to provide a
useful alternative.
It is desirable to provide a control system allowing short
distances between the vehicles of the platoon.
It is further desirable to provide a control system, which is able
to react in advance of a control point.
One or more of the objects may be achieved by the invention
according to claim 1.
In a first aspect of the present invention there is provided a
control system for travel in a platoon. The platoon comprises a
lead vehicle and one or more following vehicles automatically
following the lead vehicle. The lead vehicle controls the movement
of the following vehicles. Each of the following vehicles and the
lead vehicle comprise communication means. The control system
comprises a common time base, which allows a control command
proposing an action to be communicated from the lead vehicle to at
least one of the following vehicles in advance of a control
point.
The distance between the vehicles in the platoon is short in order
to be able to use the advantage of reduced air resistance and
thereby reduced fuel consumption. However, the vehicles are not
mechanically connected.
A control command comprises a control point t.sub.c and an action.
The control point t.sub.c is a point of time, and the accompanying
action is intended to be executed at that particular point of
time.
The desire for short inter-vehicle distances sets a precision
requirement for the common time base. The more precise the time
base is, the better precision of the control system. This makes
shorter inter-vehicle distances possible, leading to reduced air
resistance and thereby improved fuel economy. The use of a common
time base for the vehicles of the platoon facilitates short
inter-vehicle distances.
Moreover, by communicating proposed actions in advance of the
control point t.sub.c, it is possible for the vehicles to prepare
actions, e.g. pre-charge brakes, instead of reacting, that is
acting afterwards.
In an embodiment, the common time base has a precision of at least
10 ms, preferably at least 1 ms and most preferably at least 100
.mu.s.
As mentioned above, the inter-vehicle distances should preferably
be kept short. In an embodiment, the inter-vehicle distance
corresponds to a time gap between two vehicles of less than 0.6 s.
With such short time gaps, it is difficult or even impossible to
drive the following vehicle manually. Therefore, platooning makes
it possible to have shorter inter-vehicle distances as compared to
driving the following vehicles individually, especially when a
common time base is used as disclosed by the invention.
In a preferred embodiment, the common time base is based on signals
from an external clock, such as the clock of a GNSS (Global
Navigation Satellite System) e.g. GPS (Global Positioning System,
UTC time (Coordinated Universal Time) or an atomic time-based
clock. By using an external clock, the time signals may be received
simultaneously by all vehicles in the platoon. It may be
advantageous to use the GPS time, since the vehicles may anyway use
GPS for determining their positions. The use of an external time
base, which is common to all vehicles in the platoon, makes it
possible to synchronize the clock of an individual vehicle, i.e.
setting the time base of that particular vehicle, with the clocks
of the other vehicles of the platoon, especially with the lead
vehicle.
If, for some reason, the signals of the external clock cannot be
received, e.g. when driving through a tunnel, the time base of each
vehicle may be based on the last signal received from the external
clock. The lead vehicle may keep track of the clocks of the
following vehicles, and if at least one of them differs by more
than a predefined amount, the lead vehicle may send out a
synchronization signal or repeated synchronization signals, for
example once per second. As an alternative, the lead vehicle may
start sending out a time signal as soon as the contact to the
external clock is broken. The other vehicles may then synchronize
their clocks with the lead vehicle.
As an alternative, or a complement, to an external clock, the
common time base may be based on a clock of the lead vehicle,
wherein the time signal of the clock is communicated to the
following vehicles from the lead vehicle.
Preferably, the control command is adapted to compensate for
dynamic properties of the at least one following vehicle. By
adopting the control command to the actual dynamic properties of
the following vehicles and/or time delays within the platoon, the
inter-vehicle distances may be optimized. Account should be taken
of the dynamics of the vehicle having the poorest dynamics for that
particular action.
In an embodiment of the present invention, the proposed action may
comprise an action expressed as a state control over time for the
following vehicle. The control command is then provided as a
proposed action expressed as a function of time, e.g. acceleration
over time, deceleration over time, target speed over time,
inter-vehicle distance over time, steering radius over time or
position over time. The control command may be transmitted in
parameterized form, i.e. in the form of a mathematical formula, or
as a curve versus time. These types of control commands set a high
demand for precision of the time base in order to work. If the lead
vehicle instead would have sent a set of subsequent commands linked
to their respective control points t.sub.c, the following vehicles
would not understand the intention of the lead vehicle. Moreover,
the load of the communication system could also be higher,
especially if acknowledgement and execute commands are used, as
described below.
In an embodiment, it is required to acknowledge the receipt of the
control command to the lead vehicle. As an option, the proposed
action may not be carried out before the following vehicle has
received an execute demand sent by the lead vehicle.
In one embodiment of the control system, the following vehicle may,
upon receipt of the control command from the lead vehicle,
communicate to the lead vehicle, that the following vehicle is able
or unable to carry out the proposed action according to the control
command. If unable is communicated, the following vehicle may
additionally propose to the lead vehicle a possible limited state
action instead of the proposed action according to the control
command sent from the lead vehicle. The lead vehicle may then send
a new control command based on the limited state action.
Alternatively, the lead vehicle may decide to release the platoon
after first having sent a control command to increase the
inter-vehicle distances.
The control systems may further comprise a negotiation, which is
used when a candidate following vehicle wants to connect to the
platoon. The negotiation comprises sending of boundaries for state
control of the candidate following vehicle. The candidate following
vehicle may be refused to connect to the platoon, if the candidate
following vehicle has a too limited state control capability.
Moreover, the negotiation is not restricted to being used in
conjunction with the claimed control system, but could be used in
any platoon control system.
In a second aspect of the present invention, there is provided a
use of a common time base in a platoon comprising a lead vehicle
and one or more following vehicles automatically following the lead
vehicle. The lead vehicle controls the movement of the following
vehicles. Each of the following vehicles and the lead vehicle
comprise communication means. The use of the common time base
allows a control command proposing an action to be communicated
from the lead vehicle to at least one of the following vehicles in
advance of a control point.
In a third aspect of the present invention there is provided a
method for controlling travelling in a platoon. The platoon
comprises a lead vehicle and one or more following vehicles
automatically following the lead vehicle. The lead vehicle controls
the movement of the following vehicles. Each of the following
vehicles and the lead vehicle comprise communication means.
The method comprises the steps of a) establishing a common time
base. b) transmitting a control command proposing an action from
the lead vehicle to at least one of the following vehicles in
advance of a control point.
The common time base facilitates a control command proposing an
action to be communicated from the lead vehicle to at least one of
the following vehicles in advance of a control point.
Step a) is typically done on a regular basis, but it should
preferably have been done at least once before performing step
b).
In addition, the method may comprise the step of: c) the at least
one of the following vehicles acknowledging the receipt of the
control command to the lead vehicle;
and the optional step of: d) the lead vehicle sending an execute
demand.
The method may further comprise, preferably just before, just
after, in conjunction with or instead of step c), the step of: e)
the at least one of the following vehicles communicating a message
to the lead vehicle that the following vehicle is able or unable to
carry out the proposed action according to the control command.
The method may in that case skip step d).
In the case able was communicated, the method may further comprise
the step: f) the lead vehicle transmitting an execute command based
on step b).
In the case unable was communicated, the method may further
comprise the step: g) the at least one of the following vehicles
communicating to the lead vehicle a possible limited state action;
and the optional step of: h) the method returns to step b) and the
lead vehicle transmitting a new control command based on the
limited state action, or alternatively the lead vehicle releasing
the platoon;
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will hereinafter be further explained by
means of non-limiting examples with reference to the appended
figures wherein:
FIG. 1 illustrates a platoon being controlled by a control system
according to the invention.
FIG. 2 illustrates the course of events during a control
command.
FIG. 3 illustrates control commands expressed as functions of
time.
FIG. 4 illustrates a method according to the invention.
FIG. 5 illustrates inter-vehicle communication in the method of
FIG. 4.
FIG. 6 illustrates a time-control diagram of the method illustrated
in FIG. 4.
FIG. 7 illustrates another method according to the invention.
FIG. 8 illustrates a time-control diagram of the method illustrated
in FIG. 7.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The invention will, in the following, be exemplified by
embodiments. It should however be realized that the embodiments are
included in order to explain principles of the invention and not to
limit the scope of the invention, defined by the appended claims.
Details from two or more of the embodiments may be combined with
each other.
FIG. 1 schematically illustrates a platoon 1 being controlled by a
control system according to the invention. A lead vehicle L is
followed by a number n of following vehicles (F.sub.1, F.sub.2, . .
. , F.sub.i-1, F.sub.i, . . . , F.sub.n). The vehicles travel in a
procession. The number n of following vehicles is a positive
integer {1, 2, 3, 4, 5, 6 . . . }. Number i is a counter going from
1 to n. The lead vehicle L has a human driver or is run under human
supervision, while the following vehicles are not actively driven
by a driver. The lead vehicle L of the platoon controls the
following vehicles of the platoon by means of inter-vehicle
communication. The vehicles of the platoon may for example be cars,
buses, trucks or lorries.
Each vehicle has a certain distance between itself and the vehicle
being immediately in front of it. Following vehicle F.sub.1 has the
distance x.sub.1 to the lead vehicle L, following vehicle F.sub.2
has the distance x.sub.2 to the vehicle F.sub.1 just ahead, and
following vehicle F.sub.i has the distance x.sub.i to the vehicle
F.sub.i-1 just ahead and so on. The inter-vehicle distances x.sub.i
may be the same in the whole platoon, or they may vary. Preferably,
the inter-vehicle distances x.sub.i are adapted to the
characteristics of the individual vehicles, e.g. dynamic behaviour
at acceleration or braking. Further, the inter-vehicle distance may
depend on factors such as, speed of platoon, state of the road,
surrounding traffic, etc. The lead vehicle L, or more precisely the
control system of the lead vehicle, i.e. the first controller, may
determine the inter-vehicle distances x.sub.i. In a preferred
embodiment of a control system according to the invention, each
vehicle has its own controller, a secondary controller, which among
other things controls the distance x.sub.i to the vehicle just
ahead. The inter-vehicle distance x.sub.i may be determined by
means of a commonly used distance sensor, such as by laser distance
measurement, and/or by means of a GPS unit of the respective
vehicle.
The lead vehicle L controls the following vehicles by means of
control commands. A control command comprises a control point
t.sub.c and an action. The control point t.sub.c is a point of
time, and the accompanying action is intended to be executed at
that particular point of time. The lead vehicle L can send
individual control commands to the individual following vehicles F.
As an alternative, it may also send a general command comprising
control commands for two or more of the following vehicles. In that
case the control command also comprises information about which
following vehicle is intended, e.g. by using an identification
unique for each vehicle. The control commands may be continuously
updated.
The vehicles of the platoon are equipped with communication means,
here in the form of transmitters 10 and receivers 12. The lead
vehicle L may send a control command via the transmitter 10 to a
following vehicle F.sub.i proposing an action. The following
vehicle F.sub.i receives the control command via its receiver 12.
The communication between the vehicles may follow DSRC, i.e.
Dedicated Short-Range Communication, or IEEE 802.11p, p denoting a
variant suitable for vehicles. The communication between the
vehicles may also be achieved by means of cellular
communication.
As an option, the following vehicle F.sub.i may additionally have a
transmitter 10, such that itself can send messages to another
vehicle of the platoon, e.g. to the lead vehicle L, which in that
case should have a receiver 12 to be able to receive the message.
This option may be used by the following vehicle F.sub.i in order
to acknowledge the receipt of the control command sent by the lead
vehicle L. If a vehicle has both a transmitter 10 and a receiver
12, they may be combined into one transmitter-receiver unit.
The control system of the invention further comprises a common time
base. In the first embodiment of FIG. 1, this is exemplified by the
use of GPS time 3, GPS=Global Positioning System. The lead vehicle
L and the following vehicles F.sub.1, F.sub.2, . . . , F.sub.i-1,
F.sub.i, . . . , F.sub.n therefore have GPS receivers 14. Each
vehicle may thus keep track of the common time base. It is also
possible to use other external clocks, such as UTC, i.e.
Coordinated Universal Time. Preferably, an external clock should be
used, the time signals of which may be received simultaneously by
all vehicles in the platoon. It may be advantageous to use the GPS
time, since the vehicles may anyway use GPS units for determining
their positions. The receiver 12 and the GPS receiver 14 may be
combined into one receiver, possibly also combined with the
transmitter 10.
The use of an external time base, which is common to all vehicles
in the platoon, makes the clock of an individual vehicle
synchronized with the clocks of the other vehicles of the platoon,
especially with the lead vehicle. Preferably, the precision of the
clock of the individual vehicle is at least 10 ms, preferably at
least 1 ms and most preferably at least 100 .mu.s.
The above-mentioned GPS time and UTC time uses PPS, i.e. pulse per
second, and sends one pulse every second. The frequency of the
pulses is clearly defined, which makes it possible to achieve a
precision in the picosecond or nanosecond range.
The synchronization of the clocks of the individual vehicles may
also occur with a frequency determined by the lead vehicle. If the
uncertainty of a certain clock in a vehicle is known, the
synchronization frequency of that clock may be adapted to this,
such that synchronization is performed more often for a more
variable clock than for a more stable clock. The synchronization
may in that case be initialized by the lead vehicle or by the
following vehicle itself.
FIG. 1 further illustrates that the platoon 1 approaches a control
point t.sub.c, here illustrated by an X marking the corresponding
spatial position 5 of the lead vehicle L at the time t, of the
control point. In general, the following vehicles F.sub.1, F.sub.2,
. . . , F.sub.i-1, F.sub.i, . . . , F.sub.n are expected to, after
having received a control command, undertake actions required to
follow the control command. Typically, the control command is
transmitted from the lead vehicle L and received a few hundreds of
seconds to a second before execution.
FIG. 2 illustrates what happens when a control command is sent out.
Purely as an example, it is assumed that the control command
associated with the control point t.sub.c states that the vehicles
of the platoon should at the time of the control point t, start
adjusting their speed in order to achieve a desired speed
v.sub.desired. Before the vehicles can actually start adjusting
their speeds, certain time delays should be taken into account,
such as reaction time of the driver of the lead vehicle,
handshaking time for the communication of control commands to the
following vehicles and time for braking preparation, e.g. building
up braking pressure. This preparation time is denoted
.DELTA.t.sub.prep in FIG. 2 and corresponds to the platoon driving
the distance denoted by d in FIG. 1. The control command should at
the latest be transmitted at the time t.sub.c-.DELTA.t.sub.prep in
order to allow for the time delays. The time interval during which
the action is carried out is denoted .DELTA.t.sub.action, and its
length is influenced by the dynamic behaviour of the individual
vehicles. The desired speed should be achieved at the time
t.sub.c+.DELTA.t.sub.action. Account should be taken of the largest
time an individual vehicle needs for the particular desired
adjustment when selecting .DELTA.t.sub.action, since otherwise the
vehicles in the platoon would risk impacting each other.
The control commands sent from the lead vehicle L to any of the
following vehicles F.sub.t, F.sub.2, . . . , F.sub.i-1, F.sub.i, .
. . , F.sub.n may comprise an action expressed as a state control
over time, for example acceleration over time, deceleration over
time, target speed over time, inter-vehicle distance over time,
steering radius over time or position over time. In this respect
reference is made to FIG. 3, in which the x axis represents time in
milliseconds after the control point t.sub.c. Distance relates to
the inter-vehicle distance to the vehicle being just ahead.
If different control commands are in conflict with each other, for
example one command stating a certain inter-vehicle distance and
another control command stating a desired speed increase, the
control command most important for safety will be prioritized, in
this example, the inter-vehicle distance.
If, for some reason, the signals of the external clock cannot be
received, e.g. when driving through a tunnel, the time base of each
vehicle may be based on the last signal received from the external
clock. The lead vehicle L may keep track of the clocks of the
following vehicles, and if at least one of them differs by more
than a predefined amount, the lead vehicle may send out a
synchronization signal or repeated synchronization signals, for
example once per second. As an alternative, the lead vehicle may
start sending out a time signal as soon as the contact to the
external clock is broken. The other vehicles may then synchronize
their clocks with the lead vehicle.
In a second embodiment of a control system according to the
invention, the time signal forming the common time base is sent
from the lead vehicle L, for example once a second, eliminating the
need for an external clock. Preferably, the precision of the clock
of the individual vehicle is at least 10 ms, preferably at least 1
ms and most preferably at least 100 .mu.s. If the time signal from
the lead vehicle L is obscured or blocked for some reason, the time
base of each following vehicle F.sub.i may be based on the last
signal received from the lead vehicle L.
Another aspect of the invention provides a method for controlling
travelling in a platoon as shown in FIG. 4. The method comprises
the following steps, whereof some are optional as explained below
and seen as dashed boxes: 100: a) establishing a common time base;
110: b) transmitting, in advance of a control point, a control
command including the control point t.sub.c and a proposed action
from the lead vehicle L to at least one of the following vehicles
F.sub.1, F.sub.2, . . . , F.sub.i-1, F.sub.i, . . . , F.sub.n; 120:
c) the at least one of the following vehicles acknowledging the
receipt of the control command to the lead vehicle L; 130: d) the
lead vehicle sending an execute demand.
In the most general form the suggested method according to the
invention comprises only steps 100: a) and 110: b). The action is
in that case executed at the right moment thanks to the common time
base. As explained above, step a) is typically done on a regular
basis, but it should at least have been done once before performing
step b).
The method may be enlarged by step 120: c) the following vehicle
F.sub.i acknowledging the receipt of the control command back to
the lead vehicle L. In an embodiment, it is desired that all
following vehicles acknowledge their respective control commands.
As an option, the proposed action may not be carried out before the
following vehicle F.sub.i also has received an execute demand,
which in that case is sent in step 130: d).
FIG. 5 illustrates the method steps shown in FIG. 4 as
inter-vehicle communication: 110: Control commands (thin lines) are
sent to the following vehicles F.sub.1, F.sub.2, . . . , F.sub.i-1,
F.sub.i, . . . , F.sub.n from the lead vehicle L. The control
command includes the control point t.sub.c and a proposed action to
at least one of the following vehicles. A control command may be
sent to each following vehicle as illustrated. Alternatively, a
general control command may be sent comprising the control commands
for more than one, preferably all, individual vehicles. In that
case, the individual vehicles should be able to identify which
control command is intended for a certain vehicle. 120: The
following vehicles acknowledge the receipt of the control command
back to the lead vehicle L (dashed lines). 130: The lead vehicle
sends an execute command to each following vehicle, either an
individual command to the respective following vehicle (thick
lines) or a general execute command comprising execute commands for
more than one, preferably all, vehicles.
FIG. 6 is a time-control diagram of the method illustrated in FIG.
5. The time axis is directed downwards in the figure. Step a) is
independent of the other steps and may be repeated regularly as
explained above. A control command is transmitted in step b) to
each following vehicle individually and acknowledged in step c). An
execute demand is sent in step d). At the time t.sub.c, the
proposed action is carried out.
In an alternative embodiment of the method, see FIG. 7, the method
may comprise a further step instead of step c) or as a complement
to step c). Step a) and b) are as above: 100: a) establishing a
common time base; 110: b) transmitting, in advance of a control
point, a control command including the control point t.sub.c and a
proposed action from the lead vehicle L to at least one of the
following vehicles F.sub.1, F.sub.2, . . . , F.sub.i-1, F.sub.i, .
. . , F.sub.n; optional step 120: c) the at least one of the
following vehicles F.sub.1, F.sub.2, . . . , F.sub.i-1, F.sub.i, .
. . , F.sub.n acknowledging the receipt of the control command to
the lead vehicle L; 140: e) the at least one of the following
vehicles F.sub.1, F.sub.2, . . . , F.sub.i-1, F.sub.i, . . . ,
F.sub.n communicating a message to the lead vehicle L that the
following vehicle F.sub.1, F.sub.2, . . . , F.sub.i-1, F.sub.i, . .
. , F.sub.n is "able" 150 or "unable" 170 to carry out the proposed
action according to the control command. 160: f) In the case that
"able" 150 was communicated in step e) the lead vehicle may send an
execute command based on step b).
In the case that "unable" 170 was communicated in step e) the
following steps may occur: 180: g) the at least one of the
following vehicles F.sub.1, F.sub.2, . . . , F.sub.i-1, F.sub.i, .
. . , F.sub.n communicating to the lead vehicle L a possible
limited state action. 190: h) the method returning to step b) 110
and the lead vehicle L sends a new control command based on the
possible limited state action.
The lead vehicle L can at any time decide to release the platoon. A
typical situation is when "unable" is communicated from one of the
following vehicles. The release can either be total or partial.
Total release means that the platoon is split up into its
individual vehicles. The release may start from the tail end, which
is preferred in general, or anywhere in the platoon, which may be
preferred in special situations, such as an object entering the
platoon from the side, for example an elk running up on to the
road. In a partial release, the platoon may be split into one or
more sub-platoons, each sub-platoon then forming a new platoon. At
release of the platoon, the inter-vehicle distance is increased,
state control is taken over by the following vehicle being released
and an alert is sent to its driver. It is also possible to give any
vehicle in the platoon permission to release the platoon if desired
or needed.
In the case describe above, it may therefore be an alternative to
step 190 to release the platoon, if "unable" 170 is communicated in
step e).
FIG. 8 is a time-control diagram of the method illustrated in FIG.
6. The time axis is directed downwards in the figure. Step a) is
independent of the other steps and may be repeated as explained
above. A control command is transmitted in step b) and acknowledged
in step c). The following vehicles F.sub.1, F.sub.2 and F.sub.i
communicate in step e) that they are "able" to carry out the
proposed action, while one following vehicle F.sub.i-1 communicates
"unable". That vehicle also sends a possible limited state action,
step g). In step h) the method returns to step b) and the lead
vehicle sends a new control command comprising a new proposed
action considering the limited state. The following vehicles,
acknowledge the receipt, step c). This time all following vehicle
are "able" to carry out the control command, step e) and in step f)
the lead vehicle sends an execute command based on the new proposed
action. At the time t, the new proposed action is carried out.
All vehicles of the platoon may optionally be able to retransmit
control commands and act as a transponder for messages sent in
between the vehicles.
In another aspect of the present invention, the control system of
the invention also comprises a negotiation at connection of a
candidate following vehicle to the platoon. The candidate following
vehicle may enter the platoon anywhere along the platoon, but
preferably it is added at the tail end of the platoon. The
negotiation may either be initiated by the lead vehicle L or by the
candidate following vehicle. In a preferred embodiment of a control
system comprising negotiation, each vehicle has a unique identity.
Further, each vehicle has its own controller, a secondary
controller, which e.g. controls the distance x.sub.i to the vehicle
just ahead.
The negotiation is done by means of communication between the
vehicles. Thereby the lead vehicle L and the vehicle just ahead of
the candidate following vehicle are identified. The lead vehicle L
knows what other vehicles are in the platoon. Further, preferably,
each following vehicle knows at least what vehicle it has just
ahead and just behind. The candidate following vehicle also
communicates its current driving data such as position, speed and
acceleration.
The negotiation further comprises sending of the boundaries for
state control of the candidate following vehicle to the lead
vehicle. Since the lead vehicle knows the boundaries for state
control of the already connected following vehicles, the control of
the platoon can be adapted to the newly included vehicle, if the
candidate is accepted. If the lead vehicle L finds that the
candidate following vehicle has a too limited state control
capability to fit in the platoon, or if the number of following
vehicles is too high, the lead vehicle L may refuse connection of
the candidate following vehicle.
The above negotiation is suitable for the claimed control system of
the invention. However, the above negotiation, possibly including
using above-mentioned grounds for decision of allowing connection
or not, may also be useful in other control systems for platoon
driving, when a new candidate is to be connected. The negotiation
is thus not restricted to being used in conjunction with the
claimed control system, but could be used in any platoon control
system.
It is preferred to locate the lead vehicle L at the front of the
platoon as in the illustrated embodiments, but the lead vehicle can
in principle be any vehicle in the platoon.
Further modifications of the invention within the scope of the
appended claims are feasible. As such, the present invention should
not be considered as limited by the embodiments and figures
described herein. Rather, the full scope of the invention should be
determined by the appended claims, with reference to the
description and drawings.
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